Method for producing nanofibres of epoxy resin for composite laminates of aeronautical structures to improve their electromagnetic characteristics

Abstract

Composite structures and a method for improving the electromagnetic characteristics of composite structures produces epoxy nanofibres during the lay-up of structural elements of carbon fibre composite laminates. The epoxy nanofibres are fabricated by electro-spinning and may be doped with carbon nanotubes or other conducting nanoparticles. The nanofibres are selectively applied to one or more carbon fibre plys in a controlled manner of distribution.

1 . A method for producing nanofibres of epoxy resin comprising the steps of:
 a) dissolving an epoxy resin formulation in a suitable solvent; and   b) forcing the solution containing the epoxy resin formulation through at least one electrified capillary duct, wherein a meniscus is formed at the exit of the capillary duct, a charged nanojet being emitted from the vertex of the meniscus.   
     
     
         2 . The method of  claim 1  wherein the formulation of the epoxy resin is selected amongst one of the following:
 a) a liquid epoxy resin and a curing agent;   b) a liquid epoxy resin, a curing agent and a binder;   c) a solid epoxy resin;   d) a solid epoxy resin and a curing agent;   e) a solid epoxy resin and a binder;   f) a solid epoxy resin, a curing agent and a binder;   g) a liquid or solid epoxy resin partially cured with a latent curing agent; and   h) a liquid or solid epoxy resin partially cured with a latent curing agent and a binder.   
     
     
         3 . A method according to  claim 1  wherein conducting nanoparticles have been dispersed in the solution containing the epoxy resin formulation. 
     
     
         4 . A method according to  claim 3  wherein the conducting nanoparticles are carbon nanotubes. 
     
     
         5 . A method according to  claim 3  wherein a concentration of the conducting nanoparticles in the solvent is high enough to reach the percolation threshold of the solution obtained, once the solvent has substantially evaporated. 
     
     
         6 . A method according to  claim 1  wherein the at least one electrified capillary duct is part of an injection system, the solution being forced by a pumping system, the electrified capillary duct being electrified by a high voltage supply such that the electrical forces due to the high voltage supply drive the charged nanojet towards a grounded collector, thereby developing lateral hydrodynamic instabilities, which together with solvent evaporation lead to thinning of the charged nanojet. 
     
     
         7 . A method according to  claim 1  wherein the charged nanojet has a diameter that ranges from and between about 300 microns (300×10 −6  m) and about 5 nanometers (5×10 −9  m). 
     
     
         8 . A method according to  claim 1 , wherein the at least one capillary duct comprises at least two substantially concentric capillary subducts, namely an inner subduct and an outer subduct, the epoxy resin formulation being forced through a gap between the two substantially concentric subducts, a second liquid being forced through the inner subduct, such that a coaxial jet formed by an inner jet of the second fluid flowing coaxially with the epoxy resin formulation in the outer subduct, develops at the exit of the two capillary subducts to produce hollow-nanofibres. 
     
     
         9 . A method according to  claim 6  wherein there is a relative motion of the collector with respect to the injection system, resulting from a motion of the collector, or from a motion of the injection system, or from the combination of a motion of the collector and a motion of the injection system. 
     
     
         10 . A method according to  claim 9  wherein the motion of the injection system is linear and alternative, and motion of the collector is in a substantially perpendicular direction to the motion of the injection system. 
     
     
         11 . A method according to  claim 6  wherein the injection system is formed by more than one multi-injectors, each multi-injector having at least one electrified capillary duct. 
     
     
         12 . A composite laminate for aerostructures comprising a plurality of fibre plies, wherein
 at least one of the plies is coated with a layer of nanofibers;   the nanofibers are doped with nanoparticles of a high electrical conductivity;   the nanofibers are produced by the method of  claim 1 ;   and   a core material is located between any of the fibre plies, the core material being coated by nanofibers produced by the method of  claim 1 .   
     
     
         13 . A composite laminate for aerostructures having a plurality of fibre plies comprising:
 at least one fibre ply is coated with a layer of nanofibers,   the nanofibers being doped with nanoparticles of a substantially high electrical conductivity; and   the nanofibers are produced by the method of  claim 1   11 .   
     
     
         14 . A laminate according to  claim 13  wherein a core material is located between any of the fibre plies. 
     
     
         15 . A laminate according to  claim 13  wherein the core material is coated by nanofibers produced by the method of  claim 1 . 
     
     
         16 . A laminate according to  claim 13  wherein a metallic ply is located at any place in the composite laminate to improve its electromagnetic properties.